Results from the Full Analysis of CDMS Data Runs Richard Schnee Case Western Reserve University

2 DM2002 February 22, 2001 Richard Schnee - CDMS CDMS Collaboration Santa Clara University B.A. Young Stanford University L. Baudis, P.L. Brink, B. Cabrera, C. Chang, T. Saab University of California, Berkeley M.S. Armel, S.R. Golwala, V. Mandic, P. Meunier, M. Perillo Isaac, W. Rau, B. Sadoulet, A.L. Spadafora University of California, Santa Barbara D.A. Bauer, R. Bunker, D.O. Caldwell, C. Maloney, H. Nelson, J. Sander, S. Yellin University of Colorado at Denver M. E. Huber Brown University R.J. Gaitskell, J.-P. Thompson Case Western Reserve University D.S. Akerib, A. Bolozdynya, D. Driscoll, S. Kamat, T.A. Perera, R.W. Schnee, G.Wang Fermi National Accelerator Laboratory M.B. Crisler, R. Dixon, D. Holmgren Lawrence Berkeley National Laboratory R.J. McDonald, R.R. Ross, A. Smith National Institute of Standards and Technology J. Martinis Princeton University T. Shutt

3 DM2002 February 22, 2001 Richard Schnee - CDMS Detectors provide near-perfect event-by-event discrimination against otherwise dominant electron-recoil backgrounds 616 Neutrons (external source) 1334 Photons (external source) CDMS Background Discrimination Ionization Yield (ionization energy per unit recoil energy) depends strongly on type of recoil Most background sources (photons, electrons, alphas) produce electron recoils WIMPs (and neutrons) produce nuclear recoils Ionization Threshold 233 Electrons (tagged contamination) Particles (electrons) that interact in surface “dead layer” of detector result in reduced ionization yield, very good (>95%) against surface electron-recoil backgrounds bulk

4 DM2002 February 22, 2001 Richard Schnee - CDMS Detectors provide near-perfect event-by-event discrimination against otherwise dominant, very good (>95%) against surface electron-recoil backgrounds electron-recoil backgrounds bulk electron-recoil backgrounds 616 Neutrons (external source) 1334 Photons (external source) CDMS Background Discrimination Ionization Yield (ionization energy per unit recoil energy) depends strongly on type of recoil Most background sources (photons, electrons, alphas) produce electron recoils WIMPs (and neutrons) produce nuclear recoils Ionization Threshold 233 Electrons (tagged contamination) Particles (electrons) that interact in surface “dead layer” of detector result in reduced ionization yield

5 DM2002 February 22, 2001 Richard Schnee - CDMS 10.6 m earth Detectors Inner Pb shield Polyethylene Pb Shield Active Muon Veto Fridge Current CDMS Site: Stanford Expect neutron background ~2 / kg / day produced outside shield; measure using  Two materials (Si more sensitive to neutrons, Ge more sensitive to WIMPs)  Multiple-detector neutron scatters Copper Shielded, low- background environment Shallow (17 mwe rock)  Hadronic cosmic-ray flux reduced by >1000x  Muons reduced by ~5x Active muon veto  >99.9% efficient  Reject ~100 neutrons per kg-day produced by muons within shield   n n n..

6 DM2002 February 22, 2001 Richard Schnee - CDMS CDMS Results Results of runs announced at UCLA DM2000  Published in Phys. Rev. Letters v.84, #25, pp (19 June, 2000) Thesis at  1999 : 4x165 g Germanium BLIP  10.6 kg-days after cuts 13 single-scatter nuclear recoil events observed (WIMPs or neutrons) 4 multiple-scatter nuclear recoil events observed (neutrons)  1998 : 100 g Silicon ZIP  1.6 kg-days after cuts 4 nuclear recoil events observed (mostly neutrons)  Most sensitive upper limits on WIMP-nucleon cross- section Improved analysis of these runs recently completed  Relaxation of fiducial volume cut  15.8 kg-days after cuts  Better quantitative estimates of systematic errors More conservative treatment of data from 1998 Silicon ZIP  Long paper on results will be submitted soon (PRD) Description of analysis, cuts, and calculation of efficiencies

7 DM2002 February 22, 2001 Richard Schnee - CDMS Inner Ionization Electrode Outer Ionization Electrode Increasing the 1999 Run BLIP Fiducial Volume The less restrictive cut yields our “ultimate results” for the data set. Inner ionization electrode shielded from background events. Top View Region of Shared Events Events near inner-outer gap have ionization energy shared between the two electrodes Internal multiple scatters also appear as shared events Including “shared” events increases exposure  by ~40% for WIMPs  by ~60% for neutrons.

8 DM2002 February 22, 2001 Richard Schnee - CDMS 1999 Run Ge BLIP Muon-Anticoincident Data Set all single-scatters nuclear recoil candidates NR Band (-3 ,+1.28  ) 90% efficient NR Band (-3 ,+1.28  ) 90% eff. Inner-Electrode 11.9 kg-days for WIMPs 13 nuclear-recoil candidates > 10 keV Shared-Electrode 4.4 kg-days for WIMPs 10 nuclear-recoil candidates > 10 keV

9 DM2002 February 22, 2001 Richard Schnee - CDMS Neutron Multiple Scatters Require that at least one hit be in fiducial volume Observe 4 neutron multiple scatters in keV multiple events Calibration indicates negligible contamination by electron multiples  ≈1 with one misidentified  <0.05 with both misidentified neutrons Ionization Yield [keV/keV] surface electrons photons nuclear-recoil candidate in both detectors nuclear-recoil candidate in one detector  B4 / B5  B5 / B6  B4 / B6 Shared- electrod e B4 B3 B5 B6 Inner- electrod e low-yield hit in outer electrode

10 DM2002 February 22, 2001 Richard Schnee - CDMS mostly neutrons  Not WIMPs: Si cross-section too low (~6x lower rate per kg than Ge)  Misidentified electrons? Calibration predicts < 0.26 events in keV range at 90% CL, but we cannot rule out systematic error due to fact that conditions of calibration and low- background data-taking were different  Using conservative assumptions about a calibration taken under same conditions as low-background data predicts contamination of 2.2 events in NR band (<7.3 events at 90% CL)  Use this very conservative estimate (7.3 events) in calculating limits 1998 Run Si ZIP Data Set bulk events NR candidates Early-design Si ZIP measured external neutron background

11 DM2002 February 22, 2001 Richard Schnee - CDMS Consistency of Neutron Hypothesis 4 Ge multiples and 4 Si singles imply expected background of 29 neutron singles in Ge, with large statistical uncertainty x Total Shared-electrode Inner-electrode Most likely neutron background predicts fewer inner- electrode Ge multiples than seen (1.7 vs. 4). Overall, data in good agreement. Likelihood ratio test: expect worse agreement 30% of the time + Data w/ 68% confidence interval X Prediction based on Ge M, Si S Predictions based on most likely

12 DM2002 February 22, 2001 Richard Schnee - CDMS CDMS Upper Limits Most constraining upper limit of any experiment for WIMPs with GeV mass  EDELWEISS better above 70 GeV Rules out DAMA NaI/1-4 most likely point (x) at >99.9% CL (for standard WIMPs, halo) Rules out DAMA NaI/0-4 most likely point (circle) at >99% CL (for standard…) Compatible with less likely points in DAMA 3  allowed regions X marks DAMA NaI/1-4 most likely point 90% CL upper limits assuming standard halo, A 2 scaling DAMA NaI/1-4 3  region DAMA limit EDELWEISS limit Expected CDMS sensitivity

13 DM2002 February 22, 2001 Richard Schnee - CDMS Compatibility of CDMS and DAMA Likelihood ratio test  asymptotic approximations  “standard” halo  standard WIMP interactions CDMS results incompatible with DAMA model- independent annual-modulation data (left) at > 99.99% CL Best simultaneous fit to CDMS and DAMA predicts too little annual modulation in DAMA, too many events in CDMS (even for small neutron background) predicted WIMP spectrum with n background CDMS data n background (1.1 multiples) predicted WIMP modulatio n DAMA annual modulation data

14 DM2002 February 22, 2001 Richard Schnee - CDMS Compatibility of CDMS and DAMA DAMA annual modulation data predicted WIMP modulatio n Likelihood ratio test  asymptotic approximations  “standard” halo  standard WIMP interactions CDMS results incompatible with DAMA model- independent annual-modulation data (left) at > 99.8% CL, even under assumption that none of the CDMS events are neutrons Best simultaneous fit to CDMS and DAMA predicts too little annual modulation in DAMA, too many events in CDMS (even for NO neutron background) CDMS data predicted WIMP spectrum

15 DM2002 February 22, 2001 Richard Schnee - CDMS Additional Comments on Upper Limits Inner & shared electrodes Inner electrode EDELWEISS Limits from inner-electrode data are near expected sensitivity (dots)

16 DM2002 February 22, 2001 Richard Schnee - CDMS Additional Comments on Upper Limits Limits from inner-electrode data are near expected sensitivity (dots) New limits from inner-electrode data are worse than old CDMS limits (light blue) due to more conservative treatment of Si data Inner & shared electrodes Inner electrode EDELWEISS Old CDMS

17 DM2002 February 22, 2001 Richard Schnee - CDMS Additional Comments on Upper Limits QI QIS Inner & shared electrodes Inner electrode EDELWEISS Old CDMS Ignoring Si Results slightly better if Si data is ignored (dashed red curves)

18 DM2002 February 22, 2001 Richard Schnee - CDMS Additional Comments on Upper Limits Results slightly better if Si data is ignored (dashed red curves) Even without neutron subtraction (blue dash-dot curves), better limits than any other experiment for low-mass WIMPs (10-45 GeV) Inner & shared electrodes Inner electrode EDELWEISS CDMS no neutrons Old CDMS Ignoring Si (See Yellin, soon-to-be astro-ph for method)

19 DM2002 February 22, 2001 Richard Schnee - CDMS CDMS Status Data Run in progress at shallow Stanford Site  g Ge detectors and g Si detectors  Measure neutron background at Stanford simultaneously with Si & Ge ZIPs Test Monte Carlo predictions of suppression of neutron background due to addition of internal polyethelyne.  Expect about 2X increased sensitivity at shallow site  Measure contamination levels of the detectors before installation at Soudan Tower of detectors to be moved to Soudan when deep site ready Detector fabrication for second Tower is almost complete

20 DM2002 February 22, 2001 Richard Schnee - CDMS Conclusions No significant change from original conclusions  New data from relaxing the fiducial volume cut are consistent with our earlier results  Ultra-conservative treatment of Si data has small impact on results  Two years of scrutiny of the data resulted in only small changes  See long paper to be submitted very soon for (extensive) details Background is dominated by neutrons at shallow site at Stanford Best upper limits of any experiment for WIMPs with GeV mass Results incompatible with signal claimed by DAMA at high confidence level  If signal is from scalar-coupled WIMP in a standard dark matter halo We are focusing on CDMS II  First complete tower of 6 ZIPs now running at Stanford Underground Facility with internal neutron shield (factor >2)  To be transported in Soudan in Summer 2002.